1. I. INTRODUCTION III. APCI-MS Analysis Modes VI. RESULTS & DISCUSSION
Centre for Atmospheric Chemistry, York University, Toronto, Canada,
A. Jameer (ajameer@yorku.ca) and D. R. Hastie (hastie@yorku.ca)
Evaluating the Utility of an Atmospheric Pressure Chemical Ionization Mass
Spectrometer for Analyzing Organic Peroxides
References: 1. Reeves, C.E, et al., Chem. Rev, 5199-5218 (2003) 2. Crounse, J.D. et al., Anal. Chem, 6726-6732 (2006) 3.Reinnig, M., et al. Anal. Bioanal. Chem., 171-182 (2008) 4. Warscheid, B. and Hoffman, T. Rapid Commun. Mass Spectom. 496-504 (2002) 5. Rondeau, D., et al. J. Mass. Spectrom, 931-940 (2003)
ABSTRACT ID:
A23E-0308
Organic peroxides in the atmosphere are formed through the
oxidation of volatile organic compounds (VOC) by hydroxyl (OH)
and ozone (O3) radicals. These species are reservoirs for OH,
perhydroxyl (HO2) and alky peroxy (RO2) radicals and in turn,
reflect the radical levels of the troposphere.1 The presence of
these oxidants help determine the lifetime of many biogenic and
anthropogenic pollutants such as methane.1
Since organic peroxides are a potential product, numerous
analytical methods have been employed for their detection.
Most of these methods combine spectrophotometric and
chromatographic techniques which require extensive treatment
such as extraction, derivitization and/or separation before
analysis.2-4 In this study, an atmospheric pressure chemical
ionization mass spectrometer (APCI-MS) was used to determine
its ability to detect organic peroxides. Unlike the
spectrophotometric and chromatographic methods, APCI-MS
allows for fast on-line measurements and chemical
characterization without any kind of sample pre-treatments.
The ultimate goal was to develop a universal method to detect
different types of organic peroxides using the APCI-MS.
Anthropogenic and
Biogenic Emissions
VOC
O3 and OH
oxidation
Organic Peroxide
R1
O O
R2
Figure 1: Formation of organic peroxide by oxidation of anthropogenic and
biogenic emissions
II. Methodology
The mass spectra of 5 commercially available organic
peroxides were studied to evaluate the usefulness of an APCI-
MS for their detection. Peroxide standards were continuously
injected into an air stream entering the APCI-MS through the
use of a syringe pump. In the APCI-MS, peroxides underwent
chemical ionization with either protonated water or methanol
clusters. Ionization products were detected by the mass
spectrometer operating in the positive-ion mode.
Figure 2: Experimental design for detecting organic peroxides using an APCI-MS
The APCI-MS is capable of analyzing in several different
modes. Full scan (Q1 MS), product ion, and neutral loss
scan modes were utilized in this experiment to observe
the gas phase ion-molecule chemistry of selected
organic peroxides in the positive-ion mode.
Initially for organic peroxide detection, the
following reactions were believed to occur in the
ion source:
1
Q0
Q1 Q3
Detector
CEM
q2
(CID)
Triple Quad Mass Spectrometer
1. Q1 MS mode
2. Product ion scan
mode
3. Neutral loss scan
mode
Select Fragment Analyze
FragmentScan Scan
“offset value”
AnalyzeScan
Ion Source
(H2O)H+ + R1OOR2 (R1OOR2)H+ + H2O
(H2O)n H+ + R1OOR2 (R1OOR2) (H2O)n H+
(1)
(2)
Figure 3: Summary of APCI-MS analysis modes used in this experiment
IV. Results
This experiment studied the mass spectra of 5 commercially
available organic peroxides:
a)tert-butyl hydroperoxide
b)peracetic acid
c) cumene hydroperoxide
d)tert-butyl peroxyacetate
e) di-tert-butyl peroxide
Q1 MS scans for selected organic peroxides are presented
below.
Figure 4: Q1 MS scan of tert-butyl hydroperoxide
Figure 5: Q1 MS scan of tert-butyl peroxyacetate
Figure 6: Q1 MS scan of di-tert-butyl peroxide
100
80
60
40
20
0
RelativeAbundance(%)
25020015010050
m/z ratio, amu
265 ( M + M + H )
+
73 ( (CH3)3CO)
+
57 ((CH3)C)
+
V. Results
Figure 7: Q1 MS scan of tert-butyl hydroperoxide using
protonated methanol as an ionization reagent
100
80
60
40
20
0
RelativeAbundance(%) 25020015010050
m/z ratio, amu
265 (M + M + H)
+
165 (M + CH3OH + H)
+
73 ((CH3)3CO)
+
65 (2(CH3OH) + H)
+
Figure 8: Q1 MS scan of tert-butyl peroxyacetate using
protonated methanol as an ionization reagent
Ionization with (H2O)nH+ Ionization with (CH3OH)nH+
Compound Ions Observed Ions Observed
tert-butyl hydroperoxide
[M + H2O + H]+
[M + M + H]+
[M + H2O + H]+
[M + CH3OH + H]+
di-tert-butyl peroxide
[M
.
]
+
[M + H2O + H]
+
[M + H2O + H]+
[M + CH3OH + H]+
cumene hydroperoxide Fragment ions Fragment ions
peracetic acid [M + H2O + H]+ [M + CH3OH + H]+
tert-butyl peroxyacetate [M + M + H]+
[M + M + H]+
[M + CH3OH + H]+
100
80
60
40
20
0
RelativeAbundance(%)
30025020015010050
m/z ratio, amu
179 (M + CH3OH + H)
+
65 ( 2CH3OH + H )
+
146 ( M )
+
73 ((CH3)3CO)
+
100
80
60
40
20
RelativeAbundance(%)
25020015010050
m/z ratio, amu
73 ( (CH3)3CO)
+
181 (M + M + H)
+
123 ( M + CH3OH + H)
+
91(M + H)
+
100
80
60
40
20
0
RelativeAbundance(%)
30025020015010050
m/z ratio, amu
73 ( CH3)3CO)
+
181 ( M + M + H )
+
109 ( M + H + H2O )
+
100
80
60
40
20
0
RelativeAbundance(%)
30025020015010050
m/z ratio, amu
146 (M)
+
73 ((CH3)3CO)
+
57 ((CH3)C)
+
165 (M + H + H2O)
+
250
200
150
100
50
TotalIonCount10
6
543210
Time (mins)
Figure 9: Q1 MS scan of di-tert-butyl peroxide using
protonated methanol as an ionization reagent
Compound
Water as Ionization
Reagent
Methanol as Ionization
Reagent
tert-butyl hydroperoxide No Yes
cumene hydroperoxide No No
peracetic acid Yes Yes
Table 1: Summary of neutral loss scans performed on selected organic
peroxides. Organic peroxides containing a hydroperoxy group (O-O-H) exhibit
a characteristic neutral loss of 34 amu (H2O2) after protonation and collision
with CID gas during collision experiments.
100
80
60
40
20
0
RelativeAbundance(%)
30025020015010050
m/z ratio, amu
73 ( (CH3)3CO)
+
181 (M + M + H)
+
100
80
60
40
20
RelativeAbundance(%)
25020015010050
m/z ratio, amu
73 ( (CH3)3CO)
+
181 (M + M + H)
+
123 ( M + CH3OH + H)
+
91(M + H)
+
Figure 10: Q1 MS scan of pre- and post- ionization of tert-butyl hydroperoxide
with protonated methanol clusters .
Table 2: Summary of Q1 MS scans performed using protonated water or methanol
clusters during ionization.
Ionization Reagent: protonated water clusters
• Organic peroxides analyzed by the APCI-MS using
protonated water cluster as an ionization reagent yielded
unexpected results (Figures 4 – 6)
• Mass spectra were dominated by fragment ions resulting
from the cleavage of the weak peroxide (O – O) bond
during ionization
• Furthermore, ionization with protonated water clusters did
not produce [M + H]+ or [M + H + H2O]+ consistently or in
appreciable amounts (Figures 4 – 6)
• Neutral loss scan performed on organic peroxides capable
of exhibiting a characteristic loss of 34 amu (H2O2) after
protonation was only observed for peracetic acid (Table 1)
Ionization Reagent: protonated methanol clusters
• Methanol was selected as an ionization reagent since it
has the ability to generate quasi-molecular ions in the gas
phase5
• With the exception of cumene hydroperoxide, all organic
peroxides spectra showed the formation of a stable
adduct ion [M + CH3OH + H]+ (Figures 7 – 9)
• Adduct ion structures were confirmed through CID
experiments using the product ion analysis mode
• Peracetic acid and tert-butyl hydroperoxide showed a loss
of 34 amu during neutral loss scan analysis (Table 1)
Purified air flow
To dilution
flask
Syringe pump
Q0 Q1 Q3Ion source q2
Triple Quad Mass Spectrometer
M
RH+
[ M + H ]+ + R
Chemical ionization at
atmospheric pressure
Ionization reagent
VII. Conclusions
• Table 2 shows a summary of organic peroxides analyzed
using two different ionization reagents
• Results show that mostly fragment ions are observed
when protonated water clusters are used as an ionization
reagent
• Stable adducts are only observed when protonated
methanol cluster were used as an ionization reagent
M = analyte of interest
RH+ = proton-rich reagent ion
(CH3OH)H+ + R1OOR2 (R1OOR2)H+ + CH3OH
(CH3O)n H+ + R1OOR2 (R1OOR2) (CH3OH)n H+
(3)
(4)
Ionization Reagent: protonated water clusters
Ionization Reagent: protonated methanol clusters
VIII. Acknowledgements: